The present invention relates to a method or to an apparatus for establishing whether fiber material is contaminated with foreign objects.
Foreign objects in cotton are understood to include:
a) dirt and contamination; PA1 b) minerals, for example stones; PA1 c) metal parts; PA1 d) foreign fibers and foils which, for example, include packaging remnants such as jute sack remnants, plastic foil remnants, cords and bands, rags or cleaning scrim.
Currently, foreign fibers and foreign foils are the chief cause of difficulties in spinning mills, since for this category of foreign objects there is still no tested separation device. The other forms of foreign objects, for example dirt and contamination, minerals and metal parts can be satisfactorily separated out with the present state of the art, even if this is in many cases associated with a simultaneous and undesired loss of fibrous material. If, however, foreign fibers or foil remnants are present then these lead to negative effects in the spinning mill. For example, poor running behavior of the spinning machines occurs as do increased thread breakage rates, and yarn faults arise in the form of weak positions, thin and thick positions and color errors. Foreign fibers can also lead to damage to the point clothing in cleaning machines, although this is more seldom.
Various proposals have already been made as to how one can separate out the foreign fibers. Most proposals aim at splitting the fiber flocks and the foreign fibrous substances up into a stream of fibers, locating the foreign fibers and then separating out part of the fiber stream. As an example attention is directed to DE OS 36 44 535. A more recent, not yet prior published proposal of this kind can be found in the patent application filed by Maschinenfabrik Rieter AG in Switzerland on Oct. 11, 1988 with the title "Recognition of Foreign Material in Textile Fibres" Swiss patent application No. 03 803/88-4 corresponding to U.S. application Ser. No. 07/419,709 filed Oct. 11, 1989 of the present applicants' (EP - Publication Nr. 0364786). EP OS 285 602 also describes the recognition and separation out of foreign objects with a loose fibrous material having a flock weight of 10 .sup.-1 to 10 .sup.-3 g/flock, which is obtained after bale opening.